Rare earth ion size effect on T c and ϱ n in the Ga and Zn doped RBa 2Cu 3-xGa xO 7-y and RBa 2Cu 3-xZn xO 7-y systems (R=Yb,Er,Y,Dy,Gd,Eu,Sm, and Nd)

A detailed review of systematic studies on the substitution of Ga and Zn for Cu in RBa ₂Cu _3-xGa _xO _7-y and RBa ₂Cu _3-xZn _x O _7-y systems is presented (where R=Yb,Er,Y,Dy,Gd,Eu,Sm and Nd, and 0≤×≤0.3) We observed that the superconducting Tc of each system decreases approximately linearly with increasing Ga (or Zn) connet x. For a constant Ga (or Zn) content x, the T _c, the normal state resistivity ϱ _n, the critical Ga content x _O (at which the samples undergo an orthorhombic-tetragonal transition), and the melting point are dependent upon rare earth ion size. These results suggest that the decrease in the density of states N(E _F) and/or the localization of carriers, which is likely related to the Mott transition caused by Ga (or Zn) substitution, are the possible origins of the suppression of superconductivity and the observed metal-semiconductor transition.